It depends on how much you feel you need to learn. There is no reason you cannot start now and learn as you go.. just stop for side projects along the way; they are a good way to learn.
On the other hand, when you do know what you need, the game will be faster to create.
I am going to start a thread about things that people want/need to learn. I'll put the link here for you as well.
http://game-editor.com/forum/viewtopic.php?f=6&t=4938Please post a list of concepts that you need to learn to finish your game.